Known in the art is a method for transmitting discrete electrical signals in binary code from a transmitter to a receiver, interconnected by a three-wire communication line, with the communication line voltage supply source combined with the transmitter, including transmission over one wire relative to the common wire (ground) of a logic one and a logic zero from the transmitter by establishing a negative or positive voltage at its output and reading by the receiver of the value of the voltage relative to ground, and transmission of a signal using the same method over the other wire in the opposite direction with the aid of another transmitter-receiver pair. The method is known as the RS 232 interface.
A disadvantage of the known method is the low noise immunity and short communication distance, usually not more than 10 m. This is explained by the differing conditions for passage of a current in the wires of the line: the resistance in the circuit of the transmitting wires is higher than the resistance in the circuit of the common wire (ground), which contributes to emergence of a noise voltage under the influence of electromagnetic fields.
Furthermore, the method allows information to be transmitted only to one receiver, and requires that an independent bipolar electrical power supply be arranged for this, which leads to an increase in apparatus cost.
Also known is a method for transmitting discrete electrical signals in binary code from a transmitter to a receiver arranged on a three-wire communication line with the line voltage supply source combined with the transmitter, which includes the transmission of a logic one by simultaneously establishing a negative voltage in one wire and a positive voltage in the other wire relative to the third, transmission of a logic zero by establishing a close-to-zero voltage in the first and second wires relative to the logic zero of the third, and reading by the receiver of the voltage values in the first and second wires of the line. The method is known as the RS 485 interface.
The method has higher noise immunity and longer communication distance—up to 1000 m, allows a large number of devices to be interconnected and thus ensures signal transmission in both directions, but, as with the previous method, requires that an independent bipolar electrical power supply be provided for all devices connected to the line, which substantially increases the cost of the method. Furthermore, the separate power supply of the devices and longer communication distance lead to mismatch of their zero bus (ground) potentials, which may lead to the failure of instruments. To prevent this, galvanic decoupling of devices from the line is employed, which leads to additional increase in the cost of the information transmission method.
Closest in the technical essence and attainable result to the present method is a method for transmitting electrical signals via a MicroLAN bus (see, for a example Maxim “DS2409 MicroLAN Coupler”, Feb. 7, 2003; “Automatic Identification Data-Book”, Dallas Semiconductor®, 1995). The known method for transmission of discrete electrical signals from a transmitter to a receiver which are disposed on a two-wire communication line with a voltage supply source, the first pole of the source and the first wire of the communication line being grounded, while the second wire of the communication line is connected to the second pole of the source via a resistor, includes transmission of a logic signal in binary code by the transmitter closing the line with the aid of an electrical switch and the receiver reading the voltage value in the wire relative to ground. Here, a logic zero is usually considered to be a voltage level in the communication line below the first preset threshold, and a logic one—above the second preset threshold. As a rule, 0.8V and 1.2V values corresponding to logic TTL levels are chosen for such thresholds. In addition to the MicroLAN interface, many other known interfaces have been constructed in a similar manner.
The known method makes it possible to interconnect a large number of devices and to provide signal transmission in both directions over two wires, and permits the power supply of devices from the communication line, which reduces the cost of the method.
A disadvantage of the known method for transmitting discrete electrical signals is its low noise immunity. When affected by noise, though its effect is the same for both wires, the result of the effect is different, as different are conditions of propagation of noise in the grounded and non-grounded wires of the communication line, more specifically, different are resistances for flowing of the noise current in each wire from the point of effect to the pole of the power supply, or grounding. As a result, at the point of noise effect, as well as in other sections of the communication line, there emerges a voltage difference, i.e. the noise voltage, which prevents the desired signal from being transmitted appropriately.